Railway track circuits



Dec. 18, 1962 c. w. FAILOR 3,069,542

RAILWAY TRACK CIRCUITS Filed June 7, 1960 Q Q A LAJA AB J M U w j i? E 33 A: KR 'Q 1 E N B INVENTOR. UbaFZBSM TFZZZZOR BY MAW United States Patent Ofifice 3,069,542 RAKLWAY TRACK QERECUITS Charles W. Faiior, Forest Hills, Pa, assignor to Westinghouse Air Brake Company, Wilmerding, Pa, 21 corpo ration of Pennsyivauia Filed June 7, 1966}, Ser. No. 34,423 3 Qiainzs. (Cl. 246-33) My invention relates to railway track circuits, and particularly to a novel overlap track circuit arrangement for a preselected length of track in a track stretch having electrically continuous track rails.

In order to avoid the relatively great expense of installation and maintenance of insulated rail joints, it has heretofore been proposed to employ for various installations, such as highway crossing warning systems or other localized train detection systems, overlay or superimposed track circuits requiring no electrically insulated rail joints. One type of superimposed or overlay track circuit with which I am familiar comprises a transmitter tuned to a frequency in the audio range connected across the rails, and a receiver tuned to the same frequency also connected across the rails at a predetermined distance from the transmitter connections.

In single track double direction running railway territory it is sometimes desired to provide an overlap section or length of track between two adjacent sections or lengths of track, the overlap section being employed to provide a common control means for apparatus otherwise controlled individually by occupancy or nonoccupancy of each ofthe adjacent sections. One example of such an overlap section is in a highway crossing installation where the length of track spanning the highway provides for highway warning apparatus control which is common to each of the lengths of track in approach to the highway. Previously, when overlay track circuit apparatus has been employed in conjunction with such an overlap track section two sets of apparatus have been used, each set comprising a transmitter and a receiver tuned to the same frequency but to a frequency different than that to which the other set is tuned. Thus, two transmitters and receivers were required.

It is accordingly one object of my invention to provide an economical overlay track circuit arrangement employing two receivers and only a single transmitter for control of an overlap section of track and the track sections in approach to the overlap section.

It is a further object of my invention to utilize the electrically continuous rails, made possible by the use of overlay track circuits, as low frequency alternating current conductors extending to the locations of overlay track circuit receivers, at which locations such alternating current is employed in conjunction with batteries to provide direct current for operation of the receivers.

In accomplishing the foregoing objects of my invention, I provide two receivers tuned to the same relatively high frequency and connected across the rails of the extreme ends of a track stretch, and a single transmitter also tuned to that frequency, the output terminals of the transmitter being connected to opposite rails adjacent the opposite limits of an overlap track section within said stretch; and also a full-wave rectifier connected across the rails at each of the receiver locations, and a source of low frequency alternating current connected across the rails adjacent the location of the transmitter or at some location within the stretch where a source of such alternating current is available.

Other objects and characteristic features of my invention will become apparent as the description proceeds.

I shall describe one embodiment of my invention, and shall then point out the novel features thereof in claims.

3,069,542 Patented Dec. 18, 1962 The accompanying drawing is a diagrammatic view showing one form of track circuit embodying my invention.

Referring to the drawing, there is shown a length of railway track comprising electrically continuous track rails, that is, rails in which no electrically insulated joints are provided. The track length includes a track stretch comprising three track sections extending consecutively from left to right as shown on the drawing between points designated A, B, C and D. That is, points A and B designate the limits of the left-hand section of track, points B and C designate the limits of the center section of track, and points C and D designate the limits of the right-hand section of track. .These lengths of track are referred to as track sections or sections of track, but it is to be understood that the use of such terms is not intended to infer that the limits of the track sections are defined by insulated rail joints as in conventional types of track circuit arrangements.

It is expedient to point out at this time that suitable sources of direct current for control of apparatus adjacent points A, B-C, and D are provided. These sources adjacent points A and D are batteries designated 1B and 2B, respectively, employed in conjunction with rectifiers to be hereinafter discussed, and the positive and negative terminals of these batteries are designated B1 and N1, and B2 and N2, respectively. For the sake of simplicity, the direct current source adjacent points BC is not shown in the drawing but the positive and negative terminals of that source are identified by reference characters B3 and N3, respectively. There is also provided adjacent points B-C an alternating current source of a relatively low frequency such as a commercial frequency of, for example, 6 0 c.p.s. This source is also not shown in the drawing but the terminals thereof are designated BX and NX in the conventional manner.

A first output terminal 0 of a transmitter T'FU tuned to a relatively high frequency, as an example 1500 c.p.s.,

is connected to one of the rails adjacent point B, and the second output terminal d of the transmitter is connected to the other rail adjacent point C. The section of track between these staggered connections provides the overlap for control of the overlay track circuit apparatus employed in conjunction with my invention. Terminals B3 and N3 of the source of direct current at points BC are connected to input terminals a and b, respectively, of transmitter TTU to provide required direct current for operation of the transmitter. There is also connected across the rails of the track stretch adjacent points BC the secondary winding of a transformer TTR of the conventional type. The primary winding of the transformer is connected across terminals BX and NX of the alternating current source. A reactor R3 is interposed between one side of the secondary winding of transformer TTR and its connection to the rails to prevent the energy supplied to the rails from transmitter TTU from being short-circuited by the transformer.

A first set of input terminals 0 and d of each of first and second receivers tuned to the same frequency as transmitter 'ITU are connected to opposite rails of the track stretch at points A and D, respectively. These receivers at points A and D are designated ITRU and ZTRU, respectively, and their details, as well as those of transmitter TTU, form no part of my present invention but for purposes of this description such receivers and transmitters may be considered to be respectively similar to the receiver and transmitter shown and described in copending application Serial No. 778,022, filed December 3, 1958, by Philip H. Luft for Railway Track Circuit, now Patent No. 3,035,167 dated May 15, 1962, which application is assigned to the same assignee as this applica- 3 tion. While I have shown receivers lTRU and ZTRU connected directly across the track rails as shown in FIG. lb of the copending application, it is to be understood that they may be inductively coupled to the rails by wire loops as shown in FIG; la of said application.

The input terminals of a full-wave rectifier RTl are also connected to opposite rails of the track stretch at point A. A reactor R1 is interposed between one of the input terminals and its connection to one of the rails to prevent the energy supplied to the rails from transmitter TTU from intruding into rectifier RTl. The positive and negative output terminals of rectifier RTl are connected to the positive and negative terminals, respectively, of battery 13 and it is readily apparent that the alternating current supplied to the rails by transformer TTR will be rectified by rectifier RTI and in conjunction with battery 18 provides a supply of direct current for operation of receiver ITRU, the terminals B1 and N1 of battery 13 being connected to input terminals a and b, respectively, of receiver ITRU. Conductors designated 3 and 4 connect output terminals e and f of receiver lTRU across the control winding of a relay lTR located adjacent points BC. By the arrangement described, no conductors other than the track rails are necessary between point A and points B-C for supplying alternating current to rectifier RTl. A similar set of apparatus comprising a rectifier RTZ, a reactor R2, battery 2B, and receiver ZTRU is provided at point D, and conductors designated 5 and 6 connect output terminals e and f of receiver ZTRU across the control winding of a relay ZZTR also located adjacent points BC. Relays HR and ZTR are, therefore, normally maintained energized or picked-up by receivers lTRU and ZTRU receiving energy supplied to the track rails by transmitter TTU. Reference is made to said copending application Serial No. 778,022 for a complete understanding of the operation of the transmitter and receivers in maintaining the relays energized when the track stretch is unoccupied between points A and D and for a negligible distance beyond said points.

Each of the relays ITR and ZTR has a contact a operable to closed positions against front or back contact points and each of these contacts is employed to actuate control or indication apparatus which are shown in the drawing in block diagram form since the details of these apparatus form no part of my present invention. It is sufficient for purposes of this part of the description to point out that the circuits for actuating the control or indication apparatus associated with relay lTR extend from battery terminal B3 over the front or back point of contact a of relay lTR to said apparatus and to battery terminal N3. Similarly, the circuits for actuating the control or indication apparatus associated with relay 2TR extend from terminal B3 of the battery over the front or back point of contact a of relay ZTR to said apparatus and to battery terminal N3.

The operation of the system, as shown in the drawing will now be described. Since the operation of the apparatus is similar for a train movement through the track stretch in either direction only a train movement from left to right as shown on the drawing will be described.

In the unoccupied condition of the track, transmitter TTU effects current flow in the rails at a relatively high frequency (or as in the example previously set forth at a frequency of 1500 c.p.s.) which is supplied from the track rails to the input terminals and d of receivers lTRU and ZTRU. These receivers are both tuned to said frequency and are thereby operated to maintain their associated relays lTR and ZTR picked-up over the previously described circuits including conductors 3 and 4, and and 6, respectively. Thus, contacts a of relays lTR and ZTR are both normally closed against their front contact points.

At the same time, alternating current at a relatively low frequency (or as in the example previously set forth at a frequency of 60 c.p.s.) supplied to the track rails from transformer TTR, flows over the rails to points A and D,

and is supplied therefrom to rectifiers RTl and RTZ. This relatively low frequency alternating current is rectified by the rectifiers and in conjunction with batteries 1B and 2B supplies direct current for the operation of receivers lTRU and 2T RU, respectively.

Assuming now a train movement through the track stretch from left to right, the wheels and axles of the train passing point A will introduce a shunt across the rails to stop current flow from the rails to receiver ITRU, and relay lTR will accordingly be released. Also at this time the low frequency alternating current is shunted and no current flows through rectifier RT However, this operation is merely incidental since battery 1B (and also battery 28) is of sufficient capacity to provide the required direct current when the track stretch is occupied by a train. The release of relay lTR causes contact a of that relay to open its front contact point and close its back contact point and actuate the control or indication apparatus associated with relay lTR.

When the train progresses through the track stretch and passes point B, the current supplied from transmitter TTU over the track rails to receiver ZTRU is shunted, and relay ZTR is accordingly released. The release of relay ZTR causes contact a of that relay to open its front contact point and close its back contact point and actuate the control or indication apparatus associated with relay ZTR. Relay ltTR remains released at this time and will remain so until the rear wheels and axle of the train have pased beyond point C. When said wheels and axle of the train have passed beyond point D relay 2TR will again become picked-up and the apparatus again is in its normal condition. It is, therefore, apparent that the occupancy of any part of the track stretch between points A and C will release relay llTR, the occupancy of any part of the track stretch between points B and D will release relay ZTR, and the occupancy of any part of the stretch between points B and C will release both of the relays.

In View of the above description it is apparent that with the apparatus of my invention I have provided an overlap track circuit arrangement employing no insulated rail joints, and that I have provided such an overlap arrangement by employing only a single transmitter of a relatively high frequency rather than two such transmitters as heretofore employed. Further economical advantage is obtained by my invention by employing the electrically continuous track rails as conductors of a relativeiy low frequency alternating current supplied to the locations of points A and D to feed rectifiers, the output of which is employed, in conjunction with batteries at said locations, to supply direct current required for operation of the tuned receivers at the locations.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims Without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a stretch of railway track having electrically continuous track rails; first and second receivers responsive only to current of a predetermined relatively high frequency said receivers electrically connected across the rails of said stretch at first and second extreme ends of the stretch respectively and each requiring a source of direct current for their operation; means having staggered electrical connections across the rails within said stretch for supplying to the rails said current of a predetermined relatively high frequency, means having electrical connections across the rails within said stretch for supplying to the rails a current of a preselected relatively loW frequency, first and second rectifiers, a plurality of devices for blocking said relatively high frequency end, electrical connections connecting through at least one of said devices the input terminals of said second rectifier across the rails of said track stretch at said second extreme end, first and second batteries at said and second extreme ends of the track stretch respectively, means including said first and second rectifiers and said eases first and second batteries for supplying to said first and second receivers respectively the said direct current required for the operation of each receiver, first and secand relays, means controlled by said first receiver for energizing said first relay when the track stretch is un occupied between said first extreme end and the more distant of said staggered connections to the rails, and means controlled by said second receiver for energizing said second relay when the track stretch is unoccupied between said second extreme end and the more distant of said staggered connections to the rails.

2. In combination with a track stretch having a relatively high frequency current transmitter connected across the rails at a first location within the stretch and a receiver tuned to said current connected across the rails at a second location within the stretch, said receiver requiring direct current for its operation; a source of relatively low frequency current connected across the rails at said first location, a rectifier, a device for blocking said high frequency current, a circuit including said device connecting the input terminals of said rectifier across the rails at said second location, a battery at said second location, and means including said rectifier and said battery for supplying the required direct current to said receiver.

3. In combination with a track stretch having a relatively high frequency current transmitter connected across the rails at a first location within the stretch and a receiver tuned to said current connected across the rails at a second location within the stretch, said transmitterand said receiver each requiring direct current for their operation; a source of relatively low frequency current connected across the rails at one of said locations, a rectifier, a device for blocking said high frequency current, a circuit including said device connecting the input terminals of said rectifier across the rails at the other of said locations, a battery at said other location, means including said rectifier and said battery for supplying the direct current required for operation of the high frequency current apparatus at said other location, another direct current source at said one location, and means including said other direct current source for supplying the direct current required for operation of the high frequency current apparatus at said one location.

References Cited in the file of this patent UNITED STATES PATENTS 

